Professor Frederick M. Walter
Department of Physics and Astronomy
7:30 pm Room 001 ESS Building
Friday, March 1, 2013

The Disappearing Sunspots and the Coming Maunder Minimum

The Sun has been a remarkably stable star over the past 4.5 billion years, yet like all stars it does vary with time. Solar rotation, coupled with convection, drives a magnetic dynamo that reverses polarity about every 11 years. The visible dark sunspots and their approximately 11 year cycle are a manifestation of the Sun's magnetic activity. Solar magnetic activity also drives flares and coronal mass ejections, which can directly affect the Earth.

The influences of the Sun on the Earth are not all benign. On short timescales, large Solar flares can have an impact. Large flares can, and have, induced strong electric fields at the Earth, with ramifications for our fragile technological infrastructure.

On timescales of centuries, the solar activity cycle waxes and wanes. Stars like the Sun seem to spend about a quarter of their time in a low activity state. The Sun's last low activity episode, the Maunder Minimum during the 17th-18th centuries, was a time of few sunspots. The Maunder Minimum coincided with the "Little Ice Age", a time of particularly cold weather in the US and Europe. Over the past 20 years the strength of the Solar magnetic fields seems to have been declining, and the subsurface flow patterns have been changing, suggesting that the Sun may enter another minimum activity state within a decade. I shall present the evidence that the Solar cycle is turning off, and will discuss the implications for the Earth's climate.

Prof. Walter, a resident of East Setauket, studies star birth, stellar weather, and star death using the CHANDRA and XMM-NEWTON X-ray Observatories, the Hubble Space Telescope, and telescopes in Hawaii and Chile. He has been a professor of Astronomy at Stony Brook since 1989.